Carotid endarterectomy has proved to be beneficial in the prevention of stroke in selected patients. The procedure is indicated in symptomatic patients with carotid-territory transient ischemic attacks or minor strokes who have carotid artery stenosis of 70 to 99 percent. With a low surgical risk, carotid endarterectomy provides modest benefit in symptomatic patients with carotid artery stenosis of 50 to 69 percent. Platelet anti-aggregants and risk factor modification are recommended in symptomatic patients with less than 50 percent stenosis. In the Asymptomatic Carotid Atherosclerosis Study, carotid endarterectomy was beneficial in patients who had asymptomatic carotid artery stenosis of 60 percent or greater and whose general health made them good candidates for elective surgery, provided that the arteriographic and surgical complication rates were low. However, in asymptomatic patients, surgery reduced the absolute risk of stroke by only 1 percent per year.